To characterize the structure and function of the abnormal cells in the T cell leukemias. Precise identification of inflammatory cells in lesions. To study structure, function and oncological significance of the characteristic cell of the Sezary syndrome, and to study similar parameters in malignant cells of mycosis fungoides and related cancers. (1) Patients sought with Sezary syndrome and with mycosis fungoides. Specimens of blood, marrow, skin node, etc. will be obtained for study: (2) Tissue cells and buffy coat preparations will be Feulgen-stained and examined with a cytophotometer in order to detect presence of polyploid cells; (3) Tissue biopsies and buffy coat pellets will be examined with the electron microscope for morphologic identification of characteristic cells: (4) Chromosome analysis of abnormal tissue, marrow and blood cells will be made in order to determine if chromosomes are normal or abnormal in number and structure; and (5) Immunologic techniques will be used to determine whether Sezary cells belong to either B- or T-lymphocyte class. Frozen sections of tissue are layered with sheep erythrocytes containing on their surfaces moieties which will specifically interact with receptors on mononuclear cells. Histiocytes have receptor for IgC antibody and B cells have receptors for the third component of complement. BIBLIOGRAPHIC REFERENCES: Whang-Peng, J., Lutzner, M., Edelson, R. and Knutsen, T.: Cytogenetic studies and clinical implications in patients with Sezary syndrome. Cancer Research 38:861-867, 1976. Broder, S., Edelson, R.L., Lutzner, M.A., Nelson, D.L., MacDermot, R.P., Durm, M.E., Goldman, C.K., Meade, B.D., and Waldmann, T.A.: Sezary syndrome: A malignant proliferation of helper T cells. J. Clin. Invest. 58: 1297-1306, 1976.